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Search: id:A126214
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| A126214 |
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a(1)=1. a(n) = number of earlier terms, a(k) (for 1<=k<=n-1), where every integer coprime to a(k) and <= a(k) is also coprime to n. |
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+0
2
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| 1, 1, 2, 3, 4, 3, 6, 5, 6, 4, 10, 5, 12, 7, 5, 9, 16, 6, 18, 6, 9, 10, 22, 9, 12, 13, 15, 9, 28, 3, 30, 18, 14, 15, 11, 12, 36, 18, 17, 8, 40, 7, 42, 13, 9, 21, 46, 16, 21, 9, 21, 15, 52, 16, 13, 12, 26, 26, 58, 4, 60, 29, 14, 37, 14, 7, 66, 23, 29, 6, 70, 20, 72, 34, 11, 27, 20, 12, 78
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OFFSET
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1,3
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EXAMPLE
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The positive integers coprime to a(k) and <= a(k), for 1<=k<=8, are for a(1):{1}, for a(2):{1}, for a(3):{1}, for a(4):{1,2}, for a(5):{1,3}, for a(6):{1,2}, for a(7):{1,5}, and for a(8):{1,2,3,4}.
Those terms a(k), 1<=k<=8, which don't have any integers which are not coprime to 9 among those positive integers which are <=a(k) and coprime to a(k) are the six terms a(1)=1,a(2)=1,a(3)=2,a(4)=3,a(6)=3,and a(7)=6. So a(9) = 6.
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MATHEMATICA
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f[n_] := Select[Range[n], GCD[ #, n] == 1 &]; g[l_List] := Block[{fn = f[Length[l] + 1]}, Append[l, Length@Select[l, Union[f[ # ], fn] == fn &]]]; Nest[g, {1}, 80] (*Chandler*)
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CROSSREFS
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Cf. A126215.
Sequence in context: A088043 A138796 A064380 this_sequence A126801 A076945 A074792
Adjacent sequences: A126211 A126212 A126213 this_sequence A126215 A126216 A126217
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Dec 20 2006
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Dec 21 2006
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